J o u r n a l P r e -p r o o f J o u r n a l P r e -p r o o f Quality characterization of tight sandstone reservoirs in the Yanchang 1 Formation of the Honghe oilfield, Abstract: Reservoir quality is one of the important geological factors controlling the 7 development of tight oil in the Honghe oilfield, Ordos Basin, northwestern China. Analyses of 8 core, well logging, mud logging and geophysical data as well as thin sections (casting and 9 fluorescence) were combined with testing methods

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... h as grain size analysis, constant-rate 10 mercury injection, and scanning electron microscopy) to characterize the micropore-throat 11 development in reservoirs of the eighth member of Yanchang Formation in the oilfield. From 12 the perspective of sedimentation and diagenesis, the mechanisms causing reservoir quality 13 difference were explored and a method for characterizing reservoir quality difference and 14 distribution was proposed. The results show that complex and diverse pore-throat 15 configurations and multi-scale throat development are the microscale manifestations of 16 reservoir quality differences in the member. Three types of pore-throat combinations are 17 recognized, including intergranular pore-wide lamellar throat, intergranular and intragranular 18 pore-wide lamellar throat, and intergranular/clustered micropore-wide lamellar throat. 19 Different diagenesis processes and intensities under the control of sedimentary conditions 20 determine the differential development of the reservoirs. Diagenetic facies are the indicators 21 of reservoir quality. Diagenetic facies with chlorite cementation-moderate dissolution 22 indicates reservoirs with the most ideal physical properties for hydrocarbon accumulation, 23 J o u r n a l P r e -p r o o f 35 36 Ordos Basin 38 42 the oil well productivity. The productivity of reservoirs of different quality can 43 vary greatly. Therefore, the key approach to realize a successful tight oil 44 development is to enhance "sweet spot" predication by a fine characterization of 45 J o u r n a l P r e -p r o o f 3 reservoir quality. The continental tight sandstone has varying facies and poor 46 continuity. The reservoir quality inside sand bodies is highly heterogeneous. In 47 65 quality prediction methods are suitable in exploration stage; but in the 66 development stage, they are not sufficient, especially in terms of accuracy. 67 J o u r n a l P r e -p r o o f 2009) (Fig. 1). The Honghe oilfield is located in the south of Tianhuan sag of the 83 basin and covers an area of 2515.6 km 2 . Its primary oil pay zones are from the 84 Chang-8 member. The sedimentary facies are plain deposits in a shallow braided 85 river delta, which includes three types of facies, distributary channel, overflow 86 bank and distributary bay. The primary facies is distributary channel. The Chang-8 87 oil-bearing layers, mostly 2100 to 2400 m deep and 80 to 100 m thick, have an 88 J o u r n a l P r e -p r o o f Vertically, high-quality reservoirs (classes I and II) are developed in the massive 304 sandstone of Chang-8 member in the middle part of channels. Laterally, the 305 reservoirs are distributed as lens or strips along the middle and downstream of the 306 channels.